Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which seals the printhead nozzles from contaminants and drying. To facilitate priming, some printers have priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as "spitting." The waste ink is collected at a spitting reservoir portion of the service station, known as a "spittoon." After spitting, uncapping, or occasionally during printing, most service stations have a flexible wiper that wipes the printhead surface to remove ink residue, as well as any media dust or other debris that has collected on the printhead.
Servicing pens has proved quite challenging, with one suitable service station design being a rotary device first sold in the Hewlett-Packard Company's DeskJet.RTM. 850C color inkjet printer, and later in the DeskJet.RTM. 820C and 870C color inkjet printers. This rotary device mounted the wipers, primers and caps on a motor-operated tumbler. A wiper scrapper and a primer blotter were pivoted to the service station frame and rotated into contact with their associated tumbler appliances by a camming mechanism. The wiper scraper had a series of ink wicking channels which drew liquid ink residue away from the scraper tip and toward the absorbent primer blotter pad. These pens were wiped using an orthogonal wiping technique, where the wipers ran along the length of the linear nozzle arrays, wicking ink along the arrays from one nozzle to the next to serve as a solvent to break down ink residue accumulated on the nozzle plate. This rotary service station used a dual wiper blade system, with special contours on each wiper blade tip to facilitate this wicking action and subsequent cleaning of the orifice plate.
A variety of different spittoon designs have been used in the past, including single-pen and multi-pen designs, large shallow designs, and tall narrow designs having a chimney through which ink was spit for collection below the other service station components. All of these earlier designs used a fixed rigid geometry for the spittoon, which adversely impacted the overall size of the printing mechanism because most spittoons were located between the printzone and the other servicing components, increasing the overall printer width, resulting in additional cost being added to the printer, in both material and shipping costs. Moreover, this greater printer width increased the overall printer size, yielding a larger "footprint," that is, a larger working space was required to receive the printing mechanism, which was undesirable to many consumers.
Early inkjet printers used a single monochromatic pen, typically carrying black ink. Later generations of inkjet printing mechanisms used a black pen which was interchangeable with a tri-color pen, typically one carrying the colors of cyan, magenta and yellow within a single cartridge. The tri-color pen was capable of printing a "process" or "composite" black image, by depositing a drop of cyan, a drop of magenta and a drop of yellow all at the same location. Unfortunately, images printed with the composite black usually had rough edges, and the overall image, even the color portions, often had a non-black hue or cast, depending for instance, upon the type of paper used.
The next generation of printers further enhanced the images by using a dual or quad pen system. The dual pen printers provided a black pen along with a tri-color pen carrying cyan, magenta and yellow ink, with both pens being mounted in a single carriage. The quad pen printers carried four cartridges in a single carriage, while the quad pen plotters used four separate cartridges, with the four pens each carrying one color, black, cyan, magenta or yellow. These dual and quad pen devices printed crisp, clear black text while also providing full color images. Unfortunately, both the dual and quad pen printing systems produced images, such as photographic images, which had a "grainy" appearance. Inkjet printing mechanisms are known as "binary drop devices" because they form images by either placing a drop of ink on the print medium or by not firing. Not firing a droplet leaves either the print medium, or a previously printed drop(s), exposed to view. Unfortunately, such binary drop devices give inherently grainy images due to the visual "step" between the "drop on" and "drop off" regions. For example, when printing a light colored portion of an image, such as a flesh tone, yellow dots were printed and lightly interspersed with magenta dots. When viewed at a distance, these magenta dots provided a flesh tone appearance; however, upon closer inspection the magenta dots were quite visible, giving the image an undesirable grainy appearance. This grainy appearance was similar to the graininess seen in newspaper photographs, or in photos taken using the wrong speed ("ASA" or "ISO" rating) of photographic film in low light conditions.
To provide consumers with near photographic image quality, as well as crisp black text and line art, an imaging inkjet cartridge system was developed for an inkjet printing mechanism, such as the model 693 DeskJet.RTM. inkjet printer sold by the Hewlett-Packard Company of Palo Alto, Calif., the present assignee. Here, a multi-pen carriage held either a tri-chamber full color (e.g. cyan, magenta and yellow) cartridge and a monochrome (e.g. black) cartridge, or the monochrome cartridge was replaced with an imaging inkjet cartridge. While the full color cartridge carried full colorant concentrations of inks, the imaging cartridge carried ink formulations having reduced colorant concentrations, such as cyan and magenta, with either a full or a reduced colorant concentration of black ink. Of course, these new cartridges brought new challenges to meet their servicing needs.